1. Field of the Invention
The present invention relates to an electronic device formed by sealing a semiconductor device or a passive device in a resin package, and an electronic igniter.
2. Description of the Related Art
The following problems arises when sealing a semiconductor device mounted on a wiring board by flip-chip bonding in a resin package by a transfer molding process. The resin flows from all directions into a narrow region sandwiched between the semiconductor device and the wiring board, encloses a gas in a central portion of the region to form voids. The voids deteriorates the reliability of the semiconductor device. A method proposed in, for example, Japanese Patent Laid-open No. Hei 10-335386 to solve such a problem fills up the region underlying the semiconductor device with another resin. This method supplies a fluidic first resin in a resin layer onto a wiring board provided with pads by potting (or underfill) and presses a semiconductor device provided with bumps against the resin layer so that the bumps are joined to the pads, and seals the semiconductor device and the wiring board in a package of a second resin to complete an electronic device.
This method needs a first step for potting and a second step for packaging, and must select the first and the second resin so that the first and the second resin have properties suitable for the optimum combination of the resins and hence must select the resins from limited possible kinds of resins.
Accordingly, it is an object of the present invention to provide an electronic device with high reliability capable of being fabricated by a method having a small number of steps.
According to a first aspect of the present invention, an electronic device comprises at least one electronic circuit chip, such as a semiconductor device or a passive device, having first and second major surfaces, a wiring board having a first major surface on which the electronic circuit chip is mounted, a connecting part having a resin layer sandwiched between the electronic circuit chip and the wiring board, spacing the electronic circuit chip a predetermined distance apart from the wiring board and permitting the electronic circuit chip to be electrically connected to circuits formed on the wiring board, a base plate for supporting the electronic circuit chip, the wiring board and the connecting part, and a resin package sealing the electronic circuit chip, the wiring board, the connecting part and the base plate therein; wherein the resin layer and the resin package are formed of substantially the same materials, respectively.
Preferably, a recess or a through-hole is formed in the major surface of the wiring board at a position corresponding to a central portion of the electronic device.
Preferably, the volume V2 of the recess formed in the wiring board is at least 1/100 of the volume V1 of a region between the wiring board and the electronic circuit chip.
Preferably, the wiring board is formed of a ceramic material or a material in which a resin is a principal component.
According to a second aspect of the present invention, a method of fabricating an electronic device comprises the steps of: making a wiring board having a major surface; forming a recess in the major surface of the wiring board; mounting at least one electronic circuit chip on the major surface of the wiring board; and sealing the wiring board and the electronic circuit chip in a resin package.
Preferably, the step of sealing the wiring board, the electronic circuit chip in the resin package is carried out by either a transfer molding process using a thermosetting resin or an injection molding process using a thermoplastic resin.
According to the present invention, the electronic circuit chip is mounted on the major surface of the wiring board, and the recess or through-hole having an opening is formed in the major surface of the wiring board at a position in a region corresponding to the electronic circuit chip. Therefore, a gas confined in a region between the electronic circuit chip and the wiring board in the step of sealing the wiring board and the electronic circuit chip with a resin package can be collected in the recess. Consequently, any voids touching the surface of the electronic circuit chip are not formed, which enhances the reliability of the electronic device.
The step of forming the recess in the major surface of the wiring board and the step of sealing the wiring board and the electronic circuit chip in a resin package prevent the formation of voids touching the surface of the electronic circuit chip, which enhances the reliability of the electronic device.